The properties and structure of the outer membrane of Escherichia coli are being studied. Mutants altered in antibiotic sensitivity have been isolated. Mutants that map in two loci have been found to be altered in lipopolysaccharide (LPS) and not protein and lipid. Other strains have been grown under conditions where their outer membrane contained a mixture of LPS of different composition. Such membranes were found to contain domains of one or the other composition and not mixtures. To study phagocytosis in the macrophage, surface proteins have been labeled, and the cells allowed to phagocytose derivatized or unsubstituted latex beads. The labeled proteins present in the phagocytic membrane have been compared to the total labeled proteins, and differences have been analyzed. Adhesion in the macrophage differs from adhesion in other cells, since macrophages cannot be removed from surfaces by trypsin or chelators. Mutants altered in adhesion are therefore being selected from macrophage lines for further studies. Other mutants are being selected for alterations in macromolecular synthesis to see how this affects phagocytosis or adhesion.